1. Field:
The invention is in the field of foot prosthesis which attach to an amputation socket and provide an artificial leg and foot to a wearer.
2. State of the Art:
There are a number of different foot and leg prosthetic devices currently in use. The primary goal of these devices is to extend an amputated leg to the ground so as to support the wearer while upright. The earliest prior art was merely a peg secured to the amputation which provides minimal mobility to the wearer. Later, a foot was added to the bottom of the peg. An example of a more modern basic foot prosethsis known as the "Sach Foot" is a carved wooden foot with an aluminum strut attaching the foot to the amputation socket. Additional improvements made to the basic device by way of ankle hinges or ball joints, improve mobility but the overall prosthesis remains rigid and heavy and as such remains uncomfortable to the wearer. Recent studies indicate such rigid systems contribute to premature hip deterioration due to severe axial loads transmitted to the wearer's hip joint.
Recent improvements to foot prosthesis configurations utilize modern composite material technology to impart energy storage and release during use. Examples of these are the so called "Seattle Foot," which is a molded plastics foot and the prosthesis shown in U.S. Pat. No. 4,547,913, known as the Flex-Foot, which provides a composite strut and foot configuration. The spring like action imparted by the materials used results in additional mobility and comfort to the wearer. However, such prior art retains certain design characteristics which limit its potential usefulness and prevent ideal optimization possible with modern high performance composite materials. All known devices within this group are made up of individual components that must be fastened together, be it the heel-to-foot or the foot-to-connecting leg extension. These joints must be rigidly constructed so as to be strong enough to withstand the concentrated loads transmitted through them. The result is that local stiffness occurs which interferes with smooth, even flexing of the components during the wearer's stride. Even with the rigidly constructed joints, these devices are prone to fatigue and fracture at the joints thus placing the wearer at risk of injury.
In addition, composite materials exhibit poor bearing strength where fasteners penetrate the construction. The accumulative wear and erosion of structural material surrounding fasteners result in loss of position or support of attached components after a period of continual use. The fastening of the heel to the ankle portion of the foot as in U.S. Pat. No. 4,547,913 occurs at the highly stressed ankle zone. To prevent fracture, the buildup of materials required for strength makes attractive cosmetic finishing of the ankle area difficult.
With currently known prosthesis, the prosthesis is fitted directly to the amputation socket and once the prosthesis is attached to the socket, it cannot be removed. Any change of prosthesis requires a complete change of the amputation socket along with the prosthesis. The fitting of the prosthesis to the amputation socket requires careful alignment and adjustment and is thus expensive. With current prosthesis, each prosthesis must be separately fitted and secured to its own amputation socket. Because of this, many prosthesis wearers cannot afford a variety of prosthesis such as one for sporting activities, one for normal walking, and one for dress wear. Since different characteristics are desirable for prosthesis for different uses, it would be desirable for a wearer to be able to easily adjust the characteristics of a prosthesis for an intended use or to be able easily change prosthesis for the intended use. Presently, if a user engages occasionally in vigorous sports activities, his prosthesis has to be strong enough to withstand such activity. However, a prosthesis designed for active sports is generally stiffer than that required for normal walking, is uncomfortable for normal walking, and generally unsuitable for use with fashion footwear. However, a softer, more complaint prosthesis for normal wear generally cannot take the forces applied during vigorous sports activity. There is currently no prosthesis which provides a means for the wearer to adjust the characteristics of the prosthesis, and it is difficult to change the prosthesis each time an activity changes.